URGENT! H-Bridge control input problem!

I had been working on this for few weeks, and yet i couldn’t find a proper solution.
Time is ticking for submission and i’m a dead meat in few days if i cant solve this problem
I used L293D, and also L298N and the same problem still exist.

I wants my motor to move forward, so i sent High & Low for IN1 and IN2 respectively from my microprocessor. Same goes of the other half of the bridge. However, after powering the motor, i found out that the motor does not run at the desire speed. The situation goes worse when i power the VCC2 of the h-bridge with higher voltage, where one motor runs quite decently and the other one runs like turtle.

I did a few tests, and here’s my result.

  1. I swapped the motor from bridge B to A, and A to B. The same thing happens regardless. So i am crossing out faults on motor and wires connecting motor.

  2. I’ve tried capacitors to reduce noise of motors, but it doesn’t work still

  3. Both motor runs perfectly fine when i connect the h-bridge input IN1 and IN2 to 5V and ground respectively. Both motor runs at almost the same speed, so no difference in speed issue.

  4. When i measure the input signal from my microprocessor without powering the motor, it gives
    IN 1 = 5V
    IN 2 = 0V
    IN 3 = 5V
    IN 4 = 0V.
    This means the programming should be fine.

However when I power up VCC2 with the batteries, the reading becomes
IN 1 = 1.44V
IN 2 = 0V
IN 3 = 3.91V
IN 4 = 0V

Bridge A is the bridge that runs slowly, Bridge B is the bridge that runs at moderate speed.

I am guessing this might be the source of the problem?
Anyone can tell me what is actually happening and how to rectify the problem?


It sounds like you might have a power issue. What are you using as your power supply? How much current do your motors draw?

- Jeremy